The present invention relates to a threaded joint for coupling, by screwing at the end, drill rod elements, one of which is equipped at least one end with tapered male threading having a cone opening angle of less than 3.degree. and a constant threading pitch with a double screwing motion stop and of which the other is equipped with corresponding tapered female threading.
It is essential for the strength of threading used for drilling purposes to correspond at least to the static and dynamic forces of the line of rods in the hole to be drilled and to the additional stresses required during manoeuvres.
Thus, knowledge of the coefficient of safety allows the thread to be worked to its ultimate limit without difficulty when rescuing the line of drill rods.
Drilling can currently be carried out to a depth of 14,000 m.